The invention relates to an apparatus and a method for initiating the winding of webs on rolls, as well as a double pantograph frame suited to be used with said apparatus.
In general, webs such as thin polyester foils or other sheet materials are manufactured in a continuous process and the final products are wound up on rolls for storage and transportation.
However, the continuous process of manufacturing is often interrupted by breaks of the web and the winding on the rolls has to start again. One possibility is to stop the manufacturing upstream from the winding unit; this however is obviously to be avoided. In case manufacturing is continued, the part of the web that is not wound up on the roll must be taken care of. For example, one possibility for restarting a winding unit after break is to wind a certain amount of the web on an auxiliary roll or to direct this amount of web towards a chute, until the irregularities of the break are overcome and later to continue the winding on the nominal roll after cutting of the web, in a controlled manner, from the auxiliary roll or from the chute. However, the switching from the auxiliary roll or the chute to the nominal roll and the controlled cutting are complicate and time consuming and therefore expensive.
The problem is even more severe when several nominal rolls of minor size are wound up simultaneously from the same large web by splitting the web along the conveyance direction before winding. Up to now it was necessary to stop the winding of all rolls even when the break affected only one of the rolls resulting in a additional work load and higher manufacturing costs.
The problem is acute for (ultra) thin films with thickness as low as the micron size and speeds up to 1000 m/min. One solution is to blast air on a web to divert it into a winding unit, where the air blast is controlled so that the web will come at the vicinity of the nip point of two rolls, allowing starting of winding. This way of operating suffers from obvious drawbacks, i.e. harshness of the method that destroys films and difficulties for adapting the proper conditions to achieve a proper winding.
Thus, there is a need for an apparatus and a method that will allow the (re)starting of the winding of (ultra) thin films at high speed.
The object of the present invention is to provide an apparatus and a method for starting the winding of webs on winding rolls, allowing an easy and fast start/restart of the winding for one or several nominal rolls thereby reducing the work load and the manufacturing costs.
The object is achieved with an apparatus according to claim 1 and 24 and a method according to claim 29 and 37 as well as with a double pantograph frame according to claim 26. Preferred embodiments are defined in the depending claims.
The apparatus and the method as defined above have the advantage to allow an easy and fast switching from the secondary driving roll to the primary winding roll. With the secondary driving roll being an auxiliary roll and the primary winding roll being the storage roll of the final product, the invention allows for a simple and fast start up of the winding on the latter.